Beam scanning means for input/output unit

Abstract

An input and/or output unit which reads or records a picture utilizing a scanning beam in which sampling positions of picture elements in a main scanning direction are uniformly spaced. A first clock signal is produced which is at least three times as high in frequency as an output sampling clock signal. The first clock signal operates a counter, the output of which is compared with the output of a ROM. The ROM is addressed by a counter which is incremented by output comparison pulses. The output of the comparator is also utilized as the output sampling signal. Numerical values are stored in the ROM such that the output pulses from the comparator occur at times corresponding to constant sampling intervals of the scanning beam along a scanning line.

What is claimed is: 
     
       1. In an input and/or output unit for pictures which reads or records a picture with a scanning beam, the improvement comprising: a sampling signal generator for generating a sampling signal with a timing such that an interval of said scanning beam between sampling points on a scanning line is constant, said said interval being determined by a read-only memory storing numerial values corresponding to constant sampling point intervals on a scanned surface. 
     
     
       2. The input and/or output unit of claim 1 wherein said sampling signal generator comprises means for dividing a first clock for producing said sampling signal in accordance with said numerical values stored in said read-only memory. 
     
     
       3. The input and/or output unit of claim 2 wherein said numerical values stored in said read-only memory correspond sequentially to positions along a scanning line of said beam in a main scanning direction, differences between adjacent ones of said numerical values increasing towards a center position along said scanning line. 
     
     
       4. A sampling signal generating for generating a sampling signal for a beam scanning type input and/or output unit comprising: a first counter having a clock input coupled to a source of a first clock signal; a second counter; a read-only memory having address inputs coupled to count outputs of said second counter; a comparator having a first input port coupled to a count output of said first counter and a second input port coupled to a data output of said read-only memory, a comparison output of said comparator being coupled to a count input of said second counter; and an AND gate having a first input coupled to receive said output from said comparator and a second input coupled to receive a video signal. 
     
     
       5. The sampling signal generator of claim 4 wherein numerical values are stored in said read-only memory corresponding to positions of said scanning beam along a scanning line such that output pulses on said output of said comparator occur at times such that said video signal is sampled with said output of said comparator at said AND gate at times corresponding to constant sampling intervals along said scanning line. 
     
     
       6. The sampling signal generator of claim 5 wherein differences between adjacent ones of said numerical values stored in said read-only memory increase towards values corresponding to a center portion of said scanning line. 
     
     
       7. A sampling signal generator for generating a sampling signal for a beam scanning type input and/or output unit with a sampling timing such that an interval of said scanning beam between sampling points on a scanning line is constant, comprising: a read-only memory storing data values at corresponding addresses relating said sampling timing to positions along said scanning line; means for sequentially reading out said data values from said read-only memory as said scanning beam moves along said scanning line; a source of a clock signal of constant frequency; and means for varying a frequency of said clock signal in response to said data values read out from said read-only memory.